Pmmcthe permanent magnet moving coil instrument is the most accurate type for d. Thus the net effect is to increase the deflection of instrument by 0. It operates on the principle that the torque is exerted on the moving coil placed in the field of the permanent magnet. There are two types of moving coil instruments namely, permanent magnet moving coil. Various error in pmmc instrument electrical concepts. To study the advantage and limitation of pmmc instruments. The basic working principle of a pmmc instrument is the same at that d arsonval galvanometer but it slightly differs from the d arsonval galvanometer in construction. The instruments which use the permanent magnet for creating the stationary magnetic field between which the coil moves is known as the permanent magnet moving coil or pmmc instrument.
Thus we can say that the value of instrumet s much greater instrumetn the value of i m as pmmc instrument of shunt is low. Galvanometer meter is an instrument which detect very small value current, based on it operating principle it can be of many types like moving iron typegenerally. Sample ee8403 question bank measurements and instrumentation. Construction of pmmc instruments the constructional features of this instrument. Moving iron instruments principle, operation and type, theory of. Rectifier type instrument construction principle of. Sep 24, 2018 construction of pmmc instruments the constructional features of this instrument are. Advantage and disadvantages the permanentmagnet movingcoil pmmc type instruments have the following advantages and disadvantages. However the primary function of rectifier type of instruments work as voltmeter. Measurement and instruments objective questions and answers pdf free download. How the range of instrument can be extended in pmmc instruments. Moving iron instruments principle, operation and type, theory.
Instruments, types of instruments, permanent magnet moving. Electrical and electronic measurements kuestion free. Moving iron instruments are generally used to measure alternating voltages and currents. Permanentmagnet moving coil type pmmc instruments home permanentmagnet moving coil type pmmc instruments a permanentmagnet moving coiltype instrument works on the principle that when a currentcarrying conductor is placed in a magnetic field, it is acted upon by a force which tends to move it to one side and out of the field. Identify the instrument that does not exist a dynamometer type ammeter b dynamometer type. The electrical measurements notes pdf em notes pdf book starts with the topics covering control and damping torques, design considerations type of p. The moving coil is wound with many turns of enameled or silk covered copper wire. Measurements and instruments viva short questions and answers pdf. A permanent magnet is used to produce magnetic flux and a coil that carries the current. Measurement of voltage, current and power in single and three phase circuits. The construction and working of a pmmc instrument article716.
Pmmc instrument resulting deflection of the coil is indicated by a pointer that moves over a calibrated scale. Nov 09, 2017 in permanent magnet moving coil or pmmc instruments, 1c increase in temperature reduces the strength of spring by 0. Hence the temperature compensation is provided instrumemt appropriate use of pmmc instrument and shunt resistance of copper and manganin. Click here to download the pdf of this topic permanent magnet moving coil. Classification of instruments electrical measuring instruments may also be classified according to the kind of quantity, kind of current, principle of operation of moving system. Pmmc instruments, galvanometer, dc voltmeter, dc ammeter. It is one of the simple and most used instrument on board with sophisticated names.
Moving coil instruments there are two types of moving coil instruments namely, permanent magnet moving coil type which can only be used for direct current, voltage measurements and the dynamometer type which can be used on either direct or alternating current, voltage measurements. Permanent magnet moving coil instrument pmmc working and. The coils move freely in the field of a permanent magnet. Pmmc temperature compensation instrumentation tools. These notes can be downloaded easily and will definitely help you prepare well for this subject and its semester exam. Permanent magnet moving coil type pmmc instrument working principle the basic principle of operation is that when a current carrying conductor is brought in a magnetic field they should not be parallel to each other a torque on the conductor is produced. The permanent magnet moving coil instruments are most accurate type for direct current measurements. Can be constructed with very high sensitivity specially if taut band suspension is used.
Measurements and instruments viva short questions and. In pmmc meter or darsonval meter or galvanometer all are the same. Meters, double element and three element dynamometer wattmeter, errors and compensations, measurement of. Moving coil instruments permanent magnet moving coil mechanism. Engineering electronics ece electrical eee faqs measurements and instruments unit wise two marks, short, viva, interviews questions and answers pdf download. The pmmc instrument has light weight so that it can deflect rapidly.
Pmmc instruments construction and working principle. T d nbldi where n is number of turns, b is magnetic flux density in air gap, l is the length of moving coil, d is the width of the moving coil. Nov 09, 2017 permanent magnet moving coil or pmmc instruments are the most accurate type for the measurement of dc current or voltage. Moving iron instruments principle and operation repulsion type. Instruments essentials of indicating instruments permanent magnet moving coil pmmc types of instruments. A permanentmagnet moving coiltype instrument works on the principle that when a currentcarrying conductor is placed in a magnetic field, it is acted upon by a force which tends to. Meters, double element and three element dynamometer. Classification deflecting, control and damping torques ammeters and voltmeters pmmc, moving iron type instruments expression for the deflecting torque and control torque errors and compensations, extension of range using shunts and series resistance. This principle is used in moving iron attraction type instrument.
Deflecting torque in the attraction type moving iron instrument, the deflecting torque is due to the force of. Name the types of instruments used for making voltmeter and ammeter a pmmc type b moving iron type c dynamometer type d hot wire type e electrostatic type f induction type. We know that in moving coil instruments the deflecting torque is given by the expression. A permanent magnet is used to produce magnetic flux and a coil that carries the current to be measured moves in this field. Types of electrical measuring instruments absolute and. Mar 28, 2017 hi friends, on this thread i am uploading high quality notes for the subject electrical measurements and instrumentation emi. Ee8403 question bank measurements and instrumentation.
When a current carrying coil is placed in the magnetic field produced by permanent magnet, the coil experiences a force and moves. Measuring instruments classification deflecting, control and damping torques ammeters and voltmeters pmmc, moving iron type instruments expression for the deflecting torque and control torque errors and compensations, extension of range using shunts and series resistance. Permanent magnet moving coil instrument or pmmc instrument the current i is shown which breaks into two components at the point the two components are is and before i. The coil is mounted on rectangular aluminum former, which is pivoted on jeweled bearings.
Permanent magnet moving coil or pmmc instruments are the most accurate type for the measurement of dc current or voltage. Measurements and instrumentation question bank ee8403 pdf free download. The permanent magnet moving coil instrument or pmmc type. This can be avoided by using core magnet type pmmc construction. Pdf electrical measurements pdf notes em notes 2019 sw. A permanent magnet type moving coil instrument is shown in fig. Jan 15, 2019 what is a permanent magnet moving coil pmmc.
Mar 23, 2011 the permanent magnet moving coil instruments are most accurate type for direct current measurements. Current in one direction through the wire will produce a clockwise torque on the needle mechanism, while current the other direction will produce a counterclockwise torque. Construction of pmmc instruments the constructional features of this instrument are. A permanent magnet moving coil pmmc meter also known as a darsonval meter or galvanometer is an instrument that allows you to measure the current through a coil by observing the coils angular deflection in a uniform magnetic field a pmmc meter places a coil of wire i. Classification of instruments electrical instruments may be divided into two categories, that are.
Click here to download the pdf of this topic moving iron instruments. Permanent magnet moving coil mechanism pmmc mathematical. Now one question must arises in our mind why we use rectifier type of instruments. Jun 18, 2018 in order to change the range to 025 a. Permanent magnet moving coil instrument the permanent magnet moving coil instrument or pmmc type instrument uses two permanent magnets in order to create stationary magnetic field. Construction of pmmc instruments the constructional features of this instrument are shown in fig. Pmmc instrument pmmc instrument, galvanometer, dc ammeter, dc voltmeter, series ohm meter. Sep 05, 2012 instruments essentials of indicating instruments permanent magnet moving coil pmmc types of instruments. The weakening of spring can be reduced by careful use of material and preaging during manufacturing process. Hi friends, on this thread i am uploading high quality notes for the subject electrical measurements and instrumentation emi. Download practical maritime ebooks with amazing bonuses. Moving iron instruments principle, operation and type. Absolute instruments gives the quantity to be measured in term of physical constant of the instrument. The basic pmmc instrument is sensitive to the temperature.
Measurements and instrumentation questions and answers pdf free download for ece mcqs objective type interview questions lab viva manual gate cat syllabus. Here you can download the free lecture notes of electrical measurements pdf notes em pdf notes materials with multiple file links. Classification, absolute and secondary instruments, indicating instruments, control, balancing and damping, constructional details, characteristics, errors in measurement, ammeters, voltmeters. Feb 03, 2017 permanent magnet moving coil instrument the permanent magnet moving coil instrument or pmmc type instrument uses two permanent magnets in order to create stationary magnetic field. Meters, double element and three element dynamometer wattmeter, errors and compensations, measurement of unknown resistance, method of measuring low, measurement of inductance, ballistic. What is permanent magnet moving coil or pmmc instrument. A permanent magnet moving coil pmmc is one such instrument which is. The pmmc stands for permanent magnet moving coil and it is also called as darsonval instruments. Deflection torque is proportional to the square of the current. Electrical measurements pdf notes em pdf notes smartzworld. Permanent magnet moving coil instruments advantages. The pmmc instrument is wound with the silk cover copper wire between the poles of a magnet.
Permanent magnet moving coil or pmmc instrument definition. If you cannot read the numbers in the above image, reload the page to generate a new one. An ammeter has a pmmc instrument with a coil resistance of r m. Jun 20, 2018 permanent magnet moving coil instruments pmmc the permanent magnet moving coil instrument in pmmc type instrument used for measuring dc quantities only. In pmmc type instruments we use permanent magnets for create a strong stationary magnetic field. Pmmc instrument it can measure the direct current very accurately. The magnetic field strength and spring tension decrease with increase in temperature.
Feb 03, 2017 pmmc instruments, galvanometer, dc voltmeter, dc ammeter 1. Pmmc instruments, galvanometer, dc voltmeter, dc ammeter 1. For measuring several electrical parameters to analyze and keep machineries in. Let us derive a general expression for torque in permanent magnet moving coil instruments or pmmc instruments. The action of these instruments is based on the motoring principle. To understand the basic construction of movingiron instrument and its principle operation. Sep 02, 2018 construction of pmmc instruments the constructional features of this instrument are. They are used on board to assist in regular maintenance of electrical equipment or when precise measurements are required.
Permanent magnet moving coil instruments pmmc the permanent magnet moving coil instrument in pmmc type instrument used for measuring dc quantities only. Permanent magnet moving coil instruments pmmc the permanent magnet moving coil instruments are most accurate type for direct current measurements. Rectifier type instrument measures the alternating voltage and current with the help of rectifying elements and permanent magnet moving coil type of instruments. Electrical principles of operation all electrical measuring instruments depend for their action on one of the many physical effects.
These types of instruments are only used for measuring the dc quan. Name the types of instruments used for making voltmeter. Measurements and instrumentation questions and answers pdf free download for ece mcqs objective type interview questions lab viva manual gate cat syllabus skip to content engineering interview questions,mcqs,objective questions,class notes,seminor topics,lab viva pdf free download. Home permanentmagnet moving coil type pmmc instruments. Mar 16, 2018 pmmc stands for permanent magnet moving coil. Aug 18, 20 construction of pmmc instruments the constructional features of this instrument are shown in fig. In movingiron instruments the movable system consists of one or more pieces of speciallyshaped soft iron, which are so pivoted as to be acted upon by the magnetic field produced by the current in coil. The working principal of this instrument is same as that of the darsonval type of galvanometers,the difference being that a direct reading instrument is provide with a pointer and a scale. The coil resistance increases with increase in the temperature. Owing to development of materials like alcomax and alnico, which have a high co. Disadvantages of the pmmc instruments polarized external magnetic fields badly affect its operation. The working principle of pmmc instruments are same as that of darsonaval type of galvanometer, difference being that a direct reading instrument is provided with pointer and scale. Working principle and construction of pmmc polytechnic hub.
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